Here’s a possible completion of the text using the non-defining relative clauses:

At the age of fifteen Cory went on his first international trip, (1) **A who like travelling but have never tried air international travel.** Since then Cory, (2) **E which has got readers all over the world,** has travelled to over nineteen countries across five continents. Cory wrote out a list of all the places he wanted to visit. So far he’s been to the Sydney Opera House, the Blue Lagoon in Iceland, Kruger Park in South Africa and many other fascinating places. The Blue Lagoon, (3) **D whose dream has been to see the world,** has been one of his favourite adventures so far. In 2013, Cory started a travel blog, (4) **B where he went swimming in its hot sea water,** to document his adventures. He also wants to inform other disabled people in wheelchairs, (5) **C which marked the start of his life adventure,** about wheelchair-friendly destinations. Through his travelling and his blog, he wants to show that a wheelchair user doesn’t have to stay at home and give up on their dreams.